Chemical Reactions

Methanol reacts with isobutene to form MTBE. A number of secondary reactions can also occur, depending on the operating conditions and feed impurities (see Figure 4-9).

The etherification reaction is conducted in the presence of a catalyst that is cationic resin and strongly acidic. These resins are produced by sulfonation of a copolymer of polysryrene and divinyl benzene. These catalysts are very sensitive to impurities, which could destroy their acidic function, and high temperatures, which could remove the sulfonic bond. The activity of the catalyst allows operation below 195°F.

To obtain optimum yields, the reactor temperature is kept as low as possible to minimize side reactions and maximizing MTBE yield.

Table 4-22 Isomerisation Unit Feed and Product Properties Feed (Light Natural Naphtha)

FEED COMPOSITION WT FRACTION

Table 4-22 Isomerisation Unit Feed and Product Properties Feed (Light Natural Naphtha)

ISOPENTANE

0.2431

N-PENTANE

0.3616

2,2 DIMETHYL BUTANE

0.0122

2,3 DIMETHYL BUTANE

0.0225

2.METHYL PENTANE

0.0970

3,METHYL PENTANE

0.0644

N-HEXANE

0.0225

METHYL CYCLOPENTANE

0.0592

CYCLOHEXANE

0.0695

BENZENE

0.0246

C7 AND HEAVIER

0.0234

TOTAL FEED

1.0000

FEED S.G

0.6502

FEED RVP, PSI

11.30

PRODUCT PROPERTIES C4+ ISOMERATE

PROPERTY UNITS

RON MON

SPECIFIC GRAVITY

RVP PSI

C5+ ISOMERATE

PROPERTY

UNITS

RON

84

MON

81.3

SPECIFIC GRAVITY

0.641

RVP

psi

13.5

ASTM D-86 DISTILLATION

IBP

°F

91.8

10%

°F

94.1

20%

°F

97.4

50%

°F

104.4

70%

°F

127.1

90%

op

146.4

95%

°F

157.1

FBP

°F

184.4

TYPICAL MAXIMUM FEED CONTA-MINANT LEVEL (FOR CHLORINATED ALUMINA CATALYSTS)

CONTAMINANT

UNITS

SULFUR

ppmw

1

NITROGEN

ppmw

1

WATER

ppmw

0.5

OXYGENATES

ppmw

0.5

O, FEED WASH C* FEED FEED

COLUMN COALESCER DRUM

MAIN MTBE REACTOR V-005 A

MAIN MTBE REACTOR V-005 B

CATALYTIC COLUMN CATALYTIC COLUMN

V 006 REFLUX DRUM

V-007

Butene Production

Main Reaction

CH3 CH3

Methanol Isobutylene MTBE

Secondary Reactions q^

U oh

Isobutylene Water TBA

Methanol Methanol Dimethyl ether

Other Side Reactions

Butene-2 Methanol Methyl sec. butyl ether

Butene-2 Water Sec. butyl alcohol

Figure 4-9. MBTE reactions.

Pressure has no effect on the reaction, but the pressure is chosen to keep the system in a liquid phase. The pressure of the catalyst column is adjusted to keep the temperature at a minimum level and optimum conversion rate to MTBE.

Conversion increases with higher methanol at a constant temperature. However, higher methanol results in increased processing costs to recover excess methanol, and an economic optimum has to be determined between increased conversion and increased production cost.

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